Diffusion testing is a release rate test of an active pharmaceutical ingredient in semisolid form as it permeates through a skin-like or synthetic membrane into solution. Diffusion replicates the process of skin-applied medicine as it permeates the skin into the body for local or systemic action. It is ideal for the quality control of topical preparations. Semisolid preparations such as creams, ointments, and gels must penetrate the layers of the skin to have benefit. Topical pharmaceutical formulations, designed to permeate the skin, require in vitro release-rate testing that can produce reliable and consistent results. Diffusion testing measures the rate that an active pharmaceutical ingredient is released from a semisolid preparation, providing the quality control analyst with critical performance data. Diffusion testing using diffusion cells has become the industry standard due to the pioneering work of Dr. T. J. Franz who developed the “Franz cell.” This device consists of a small-volume, water-jacketed cell that contains a chamber for drug application, a membrane through which the drug may permeate, and a receptor media chamber from which samples may be extracted and analyzed for drug release. The chamber for drug application, however, often times suffers from imprecise manufacturing resulting in misalignment of components in the drug application chamber, which causes variations in results across test samples in the same batch.
A traditional diffusion testing system typically has a group of six cells for simultaneous testing of six specimens. A magnetic cell drive controls the mixing of each cell receptor chamber throughout the test, and a circulating bath provides heated water to the jacketed cells to maintain temperature. As such, traditional diffusion systems occupy a large footprint, have inefficient control of temperatures due to the water bath, create large variances in results due to imprecisions in the diffusion cells, and are difficult to automate. For the foregoing reasons there is a need for an improved diffusion system to address these issues.